Impedance matched antenna apparatus



Aug. 11, 1959 G, E. STETSON 2,899,678

IMPEDANCE MATCHED ANTENNA APPARATUS Filed March 20, 1957 Tag.;

25' i 5 /4 23 .Y /a /7 E? Z9 5/ INVENTOR ATTO NEY UnitedStates Patent OllVlPEDANCE MATCHED ANTENNA APPARATUS Gerald E. Stetson, Buzzards Bay,Mass., assignor to Colonial Aircraft Corporation, Sanford, Maine, acorporation of New York Application March 20, 1957, Serial No. 647,317

2 Claims. (Cl. 343-864) The instant invention relates to antennastructure, and in particular, to impedance matched ground plane antennaapparatus designed to achieve eiiicient operation.

Antenna structure for the VHF communication bands tend to becomestructurally and electrically complexed to secure efcient standing waveratio operation, to avoid radiation losses and to achieve over-allsystem efficiency. Heretofore, economy of manufacture was sacrificed andin addition, highly technical installation personnel were used toinstall antennas so that optimum antenna operation would be realized.

It is a principal object of the instant invention to provide a groundplane antenna structure that assures efficient standing wave ratiooperation for the VHF communication bands, which structure includes anantenna housing adapted to couple the antenna to a load withoutradiation loss. The housing is also provided with tuning means formaintaining an impedance match over the operating frequency band and byvirtue of its novel design permits economy of manufacture, ease ofassembly, and installation by inexperienced personnel withoutsacrificing optimum operation over the desired band width.

It is a further object of the instant invention to provide novel antennastructure in which all conducting elements of the antenna are maintainedat the same D C. potential and all connected directly to the supportingmast. By grounding the mast upon which the antenna is mounted, theentire antenna is protected against lightning without the use of speciallightning arrestors thereby providing a safety measure for theprotection of operating personnel and equipment.

It is a further object of the instant invention to provide novel antennastructure having a tunable coaxial line transformer and a radiator tocoaxial line transition wherein radiation losses are avoided andover-all low standing wave operation of the system is maintained therebypermitting reception of weak signals with usable strength.

It is a further object of the instant invention to pro vide novelantenna structure wherein an antenna housing is accommodated by a novelarrangement for coupling a tunable transformer thereto to maintain animpedance match thereby assuring eliicient standing wave ratiooperation.

Other objects and advantages will become apparent upon reading thefollowing description taken in conjunction with the figures, in which:

Fig. l is a longitudinal elevation, in section, showing antennastructure incorporating the improvements of the invention;

Fig. 2 is a top plan view of the antenna; and

Fig. 3 is a fragmentary and sectional view of the antenna housingshowing certain details thereof.

Referring to the igures, an impedance matched ground plane antenna ismade up of a longitudinally extending hollow lower radiator rod and anupper radiator rod -11. Rod 10 is fixed to an antenna housing 12,whereas rod 11 may be slidably adjusted toextend from or re- ICCVdiametered lower portion 16 longitudinally depending from upper portion15. Member 14 has a through bore 17 into which base y18 of rod 10extends coaxially. The upper end'of bore 17 is threaded. A mounting nut19 is coaxially mounted over base 18. Nut 19 is provided with a threadedouter surface 20 in register with threaded part of bore 17. Mounting nutV19 has a radial flange 21 bearing against the upper end of member 14.The contiguous surfaces of ange 21 and member 14 are at to facilitateabutment. Base 18 of rod 10 is provided with spaced apart annularrecesses 22, 23. Recesses are juxtaposed at upper and lower end faces ofnut 19. A pair of split-spring-snap-on retainers 24, 25 register withinrespective recesses and overlap, respectively, the upper andlowersurfaces of mounting nut 19 to lock radiator 10,11 againstlongitudinal motion.

A cylindrical, hollowed, electrical conducting body 27 encircles smallerdiameter part 16 of member 14 and cooperates therewith to define partof. the antenna housing 12. vRecessed screws 28 hold member 14 and body27 together.

Bore 17 develops into a relatively large cavity 29 in the intermediateportion of member 14. Conducting body 27 has a transverse throughpassage 30, the inner end of which communicates with cavity 29. Acircular electrically conducting coupling unit 31 provided with athrough passage is mounted over the portion of radiator base 18 in theregion of cavity 29. Coupling unit 31 is vertically Vpositioned andfastened to base 18 by set screw 32 and cooperates with conducting body27 to define a coaxial line T junction in cavity 29. A threadedtransverse through aperture is provided in unit 31 for set screw 32 toenable the inner end thereof to bite against base 18 of radiator. Alateral through aperture 5,0 in bodies 16 and `27 provides accessibilityto set screw 32 when attaching unit 31 to antenna base 18. Coupling unit31 also has a transversely extending tubular rod 33 projecting throughpassage 30 and beyond the outer entrance thereof. An electric conductinghollow outer tube 34 has an opened end held fast to the entrance ofpassage 30. Tube 34 is suspended coaxially about rod 33. v

The terminating ends of rod 33 and tubular body 34, i.e., the endsthereof spaced from housing 12 are provided with an adjustableelectrical short to define a coaxial tuning transformer. The transformeris at least 1A wave length at the lowest operating frequency. The shortcomprises an electrical conducting en-d plate 35 having an outwardlyextending ange 36 slidably engaging the inner bore of tubular body 34, acentrally disposed aperture 37 through which rod 33 extends, and athreaded screw 38 fastened to plate 35 and threaded to Vone of the pairof anchoring nuts 39 sweated to the inner conductor rod 33 and outertube 34. A 90 bend 55 in transformer line provides a compact,symmetrical antenna radiator structure for operation over thecommunication bands. In practice, it has been found that one antenna iscapable of covering 30 to 70 mcs. while another scaled antenna willcover to 170 mcs. 'Ihe tuning transformer matches the antenna to a loadover vthe frequency band of operation.

The lower end of housing 12 is enclosed by a circular electricalconducting terminal block 40 having an upwardly extendingcircumferential flange 41 projecting over the outer lower surface ofconducting body 27. Block 40 is held to body 27 by screws 42. The lowerends of coaxial bodies 27` and 16 nest in the seat created at the upperside of terminal block 40.

The lower end of bore 17 is stepped diametered to receive a tightlyfitting washer 43 which cooperates with mounting nut 19 to maintainantenna base 18 in firm coaxial alignment within bore 17. Terminal block4t) has a centrally disposed through passage defined by successive bores44- and 44a of different diameters. The smaller diametered bore 44receives a coaxial connector 45 flange fastened to the lower face ofterminal block 40 by screws 46. An inner conductor 47 of the coaxialconnector 45 is electrically connected to the lower end of fixed rod 10by a flexible wire 48 extending through bore 44a. Threaded bolt 49secures wire 48 to rod 10.

Conducting body 27 cooperates with the portion of radiator base 18extending therethrough to dene a coaxial line, which coaxial lineterminates in a plane A substantially coplanar with the upper end ofcylindrical body 27, to establish a coaxial line to radiator transition.Furthermore, the inner surface of bore 44a and flexible wire 48 may beconsidered to be a section of coaxial line coupling connector 45 torelatively larger diametered line having body 27 as its outer conductor.The transition will provide smoother electrical characteristics if thediameter of bore 44a is enlarged to a size comparable to the diameter ofinner bore surface of body 27, due to the electrical capacities presentbetween body 27 and rod 10 and between terminal block 40 and rod 10, andis so illustrated herein. The coaxial line tuning transformer in eiectcontinues to and terminates Iat the T junction, consequently, it is seenthat there will be no radiator or energy leakage along this line oralong the line from plane A to connector 45, which is a continuouscoaxial transmission line.

The ground plane reector may be established by mutually spaced apartradials; four radials electrically approximately l@ wave length long arecounterpoised to simulate the ground reflector in the illustratedembodiment. Radials 51 are threaded at inner ends to conducting body 27and are disposed to lie in a horizontal plane as close to plane A asmechanically convenient.

A mounting adaptor 52 is fastened by bolts 53 to body 27 and coversaperture 50. Adaptor 52 is provided with U bolts S4 designed to engage astandard antenna mast (not shown). Accordingly, all the components ofthe antenna are at the same D C. potential and all being connecteddirectly to the supporting mast. 'Ihus by simply assuring that the mastupon which the antenna is mounted has been well grounded, the entireantenna is protected against lightning without the use of speciallightning arrestors or other methords. This provides an excellent safetymeasure for the protection of operating personnel and equipment.

As noted hereinbefore, bend 5S improves the symmetry of the antennaphysically, but primarily it is to bring the transformer tuningadjustment screw 38 below the plane of the ground radials 51, thusgreatly reducing the capacitive effect of the body of a person makingadjustments on the antenna. Being effectively 1/4 wave length below theground radials and electrically shielded from the radiator 10, 11,adjustment screw 38 may be approached by installation personnel withoutseriously disturbing the electrical characteristics of the antenna.Thus, the antenna can be shipped from a factory pretuned, and the usercould readily re-tune the system without special equipment orconsiderations.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it isintended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Antenna structure comprising, an adjustable longitudinally extendableand retractable antenna radiator having a lower base portion, aninsulated member having a large diametered upper portion and a smallerdiametered lower portion depending longitudinally therefrom, said memberhaving a through bore into which said base extends coaxially, anelectrical conducting body encircling said smaller diametered part ofsaid member and cooperating therewith to define an antenna housing,means latching said radiator to said housing to lock said radiatoragainst longitudinal motion, said bore developing into a relativelylarge cavity in the intermediate portion of said member, said bodyhaving a transverse through passage, the inner end of said passagecommunicating with said cavity, radiator reecting means electricallyconnected to said body, an electrical conducting coupling unit attachedto said base portion of said antenna in the region of said cavity andhaving a radially extending tubular rod projecting through said passageand beyond the outer entrance thereof, a hollow tubular electricalconducting body having an open end fixed to said passage and beingcoaxially disposed about said rod, an adjustable electrical short at theends of said rod and tubular body spaced from said housing and definingan adjustable tuning transformer, an electrical conducting terminalblock mounted at the lower end of said housing and having a throughaperture aligned with the lower bore end, and connector means mounted atsaid aperture and enclosing said bore for electrically coupling saidradiator to a load.

2. Antenna structure comprising, an adjustable longitudinally extendableand retractable radiator having -a lower base portion, an insulatedmember having a large diametered upper portion and a smaller diameteredlower portion depending longitudinally therefrom, said member having athrough bore into which said base extends coaxially, the upper end ofsaid bore being threaded, a mounting nut coaxially mounted on said basehaving spaced apart upper and lower surfaces, said nut having an outersurface threaded to the threaded part of said bore, said base havingspaced apart annular recesses, each recess being juxtaposed respectiveupper and lower surfaces of said nut, split spring retainers registeringwithin said recesses and overlapping said upper and lower nut surfacesto lock said radiator against longitudinal motion, said bore developinginto a relatively large cavity in the intermediate portion of saidmember, an electrical conducting body encircling said smaller diameteredpart of said member and cooperating therewith to define an antennahousing, said body having a transverse through passage, the inner end ofsaid passage communicating with said cavity, an electrical conductingcoupling unit attached to the portion of said base in the region of saidcavity and having a radially extending tubular rod projecting throughsaid passage and beyond the outer entrance thereof, an electricalconducting reliecting plane connected to said body, a hollow tubularelectrical conducting body having an open end axed to said passage andbeing coaxially disposed about said rod, an adjustable electrical shortat the terminating ends of said rod and tubular body and defining anadjustable tuning transformer, an electrical conducting terminal blockmounted at the lower end of said housing and having a through aperturealigned with the lower bore end, coaxial connectormeans mounted at saidaperture and enclosing said bore, and means connecting the innerconductor of said connector to the lower end of said radiator.

References Cited in the le or" this patent UNITED STATES PATENTS BrownMar. 11, 1941 OTHER REFERENCES

